1. Field of the Invention
This invention relates to a process for preparing an .alpha., .beta.-unsaturated carboxylic acid ester, more particularly to a process for an efficient production in an industrial scale of an .alpha.,.beta.-unsaturated carboxylic acid ester by using an .alpha.-hydroxycarboxylic acid ester as the starting material.
The .alpha.,.beta.-unsaturated carboxylic acid ester is very useful in industry as a starting material for synthetic resins. In particular, methyl methacrylate obtained from methyl .alpha.-hydroxyisobutyrate has been used for an important industrial purpose, as a starting material for polymethyl methacrylate which has excellent weather resistance and transparency.
2. Description of the Related Arts
The present inventors' group previously disclosed a process for preparing an .alpha.,.beta.-unsaturated carboxylic acid and/or an ester thereof by using at least one ester selected from the group consisting of .alpha.-hydroxycarboxylic acid ester, .alpha.-alkoxycarboxylic acid ester and .beta.-alkoxycarboxylic acid ester as a starting material, and by catalytically reacting it with crystalline aluminosilicate catalyst (Japanese Patent Application Laid-Open No. 196753/1990).
Although the above process is remarkably efficient, .alpha., .beta.-unsaturated carboxylic acid and an ester thereof are produced simultaneously. Accordingly, operations for separating and recovering these products, such as distillation and extraction, are inevitable in the process. Since these operations cause an increase in production cost, more simple and economical process is desired to be developed.